Arachidonic acid intestinal absorption: Mechanism of transport and influence of luminal factors on absorption in vitro

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Abstract
The mechanism and characteristics of intestinal absorption of arachidonic acid were studied in vitro using everted intestinal sacs of the rat. Arachidonic acid absorption was studied at concentrations of 5 .mu.M to 8.36 mM. The plot of absorption rate vs. concentration fitted best to a rectangular hyperbola at low .mu.M concentrations and to a straight linear relationship in the mM range of concentrations. Metabolic inhibitors and uncouplers did not change absorption in either range of concentrations. The absorption of arachidonic acid increased with thinning of the unstirred water-layer, decreased in the pH or the substitution of sodium taurocholate by Pluronic F 68 or Tween 80. Absorption decreased following the equimolar additions of oleic, linoleic and linolenic acids. Absorption rate did not change when the taurocholate concentration was varied from 5-15 mM or following the additions of butyric or glutamic acids, leucine, lysine or dextrose. Arachidonic acid is absorbed by a concentration-dependent dual mechanism of transport which is not energy dependent. At the low .mu.M range of concentrations, facilitated diffusion is predominant, while at mM concentrations, simple diffusion is the dominant mechanism of absorption. Changes in the intestinal fluid composition, flow rate and pH can modify the rate of absorption of arachidonic acid. [Arachidonic acid was discussed as a metabolic precursor of prostaglandins].